Download West Nile Encephalitis Fact Sheet

West Nile Virus Disease Fact Sheet
What is West Nile virus disease?
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West Nile disease encompasses a spectrum of illness
which can result in becoming infected with the West Nile
virus.
West Nile virus (WNV) is transmitted to people and
horses through the bite of a mosquito infected with the
West Nile virus. In Minnesota, Culex tarsalis, a common
mosquito in agricultural regions of western and central
Minnesota, is the most important vector in transmitting
WNV to humans.
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Most people infected with WNV will have no symptoms
(70-80%). One in five people have a relatively mild
illness with fever. A small percentage of people (<1%),
especially elderly patients, may develop meningitis or
encephalitis (inflammation of the central nervous system,
including the brain). Approximately 10% of these
encephalitis cases are fatal.
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WNV is maintained in a transmission cycle involving one
or more species of mosquitoes and birds.
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WNV was historically found in Africa and southern
Europe. The virus was first reported in North America
during a 1999 outbreak of encephalitis in New York City.
What is the risk of a West Nile Encephalitis outbreak
in Minnesota?
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Since 1999, WNV has become established in all 48 states,
the District of Columbia, and all Canadian Provinces.
WNV was first detected in Minnesota July 23rd, 2002.
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From 1999-2012, 16,196 (1,549 deaths) human WN
meningitis and encephalitis cases were reported in the
United States. Including more mild WN fever cases, 535
(16 deaths) WNV disease cases have been reported in
Minnesota residents.
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With our abundant mosquito and bird populations, WNV
has rapidly become established in Minnesota. Similar to
other mosquito-transmitted diseases previously
established in this area (LaCrosse encephalitis, Western
equine encephalitis, and Eastern equine encephalitis),
WNV will cause sporadic illness in humans (especially
elderly people) and horses.
What can people do to prevent West Nile
Encephalitis?
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Personal protection measures such as use of mosquito
repellents (containing up to 30% DEET), avoiding
outdoor exposures at dusk and dawn (peak feeding time
for many mosquitoes), and wearing long-sleeved shirts
and long pants can reduce the risk of WN disease.
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Removal of water-holding containers (mosquito breeding
sites) from residential areas will reduce numbers of
several mosquito species.
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There is a vaccine available for horses to prevent WN
encephalitis. Please contact your veterinarian for vaccine
recommendations. However, there is no WN disease
vaccine for humans.
How serious is West Nile virus?
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Most of the severe human cases of WN disease begin with
a sudden onset of fever, headache, neck stiffness, and
vomiting. The illness progresses quickly to include
confusion and other mental status changes, altered
reflexes, convulsions, and coma. There is no treatment for
WN Encephalitis other than supportive care.
Minnesota Department of Heath
Infectious Disease Epidemiology, Prevention, and Control Division
PO Box 64975, Saint Paul, MN 55164-0975
651-201-5414 or 1-877-676-5414
www.health.state.mn.us
July 2013